The invention relates to an optical disc comprising a recording area for recording data at a substantially constant density, the recording area comprising circular or spiral tracks provided with a servopattern comprising headers alternating with track portions, the headers being radially aligned and comprising position information, and the track portions being arranged for storing an amount of data substantially proportional to the radial position of the track portion concerned.
The invention further relates to a recording device for recording data at a substantially constant density on an optical disc comprising a recording area comprising circular or spiral tracks provided with a servopattern comprising headers alternating with track portions, the headers being radially aligned and comprising position information, and the track portions being arranged for recording an amount of data substantially proportional to the radial position of the track portion concerned, which device comprises a recording head, recording control means and positioning means for positioning the recording head on a track at a position to be recorded, the positioning means comprising header detecting means for retrieving the position information from the headers.
The invention further relates to a reading device for reading data from an optical disc recorded at a substantially constant density, the optical disc comprising a recording area comprising circular or spiral tracks provided with a servopattern comprising headers alternating with track portions, the headers being radially aligned and comprising position information, and the track portions comprising an amount of data substantially proportional to the radial position of the track portion concerned, which device comprises a reading head, reading control means and positioning means for positioning the reading head on a track at a position to be read, the positioning means comprising header detecting means for retrieving the position information from the headers.
Such a record carrier and apparatus are known from European Patent Application EP 0 587 019, document D1 in the list of related documents. The document discloses a record carrier in the form of an optical disc having a recording area comprising a pattern of grooves on a substrate, constituting a servopattern of circular or spiral tracks. The recording tracks are subdivided in longitudinal direction into track portions alternating with headers. The headers comprise position information, e.g. an address area comprising pre-recorded address marks. The headers are made during manufacture, e.g. in the form of so-called pre-pits formed by embossing. The address marks represent position information for positioning a recording head on a desired track and are indicative for the address of the recording area following the address area. In a direction transverse to the tracks, i.e. radially, the headers are aligned. The disc comprises one track address and a fixed number of radially aligned servo pits in each turn, constituting a so-called sampled servo pattern. The servo pattern comprising radially aligned elements is called Constant Angular Velocity (CAV) servo pattern, and is to be scanned by a servo system having a phase locked loop (PLL) to generate a servo frequency locked to the rotation frequency of the disc. The address marks are dimensioned to be read clocked by said servo frequency. Further a data phase locked loop is provided for generating a data clock locked to a speed of data read/write operations, which are performed at a substantially constant linear density. Each track portion is arranged for recording an amount of data substantially proportional to the radial position of the track portion concerned. Hence the density is substantially constant across the whole recording area, which corresponds to the well-known constant linear velocity (CLV) system. When jumping to a new radial position, the rotation frequency setting point or the data clock setting point are adjusted to the new position, but the servo phase locked loop remains locked to the CAV servo pattern. Hence the addresses in the headers can always be read at the servo frequency. The recording apparatus comprises an optical system for recording or reading information by generating a spot via a radiation beam on a track of the record carrier. The optical disc is rotated and the spot is positioned in radial direction on the centre of the track by servo means for scanning the track. During scanning the servo phase locked loop is locked to the rotation frequency of the disc for reading the CAV servo pattern. The data phase locked loop is locked to the CLV data speed. The known record carrier and apparatus have the problem, that for reliable operation a first phase locked loop must be locked to the CAV servo pattern, and a second phase locked loop must be locked to the CLV data density.
It is an object of the invention to provide an optical disc, a recording and a reading device arranged for a more reliable data recording and/or retrieval operation while data is recorded at a substantially constant density.
For this purpose an optical disc as described in the opening paragraph is characterized according to the invention in that the position information is provided substantially at said constant density. This has the effect, that the headers are positioned on locations corresponding to a CAV pattern, but have an information content readable by the data clock. There is no need for a second phase locked loop, only one phase locked loop locked to the data frequency is required. Hence, the recording is less complex and more reliable. This is also advantageous in that the space required for the header pattern is reduced when compared to a CLV header pattern, as shown for example in FIG. 2 and described below. Hence the header overhead is reduced, which increases the effective data storage capacity of the disc.
For the purpose mentioned above a recording device as described in the opening paragraph is characterized according to the invention in that the header detecting means are arranged for reading the position information substantially at said constant density. A reading device as described in the opening paragraph is characterized according to the invention in that the header detecting means are arranged for reading the position information substantially at said constant density. This has the effect, that the headers, although positioned corresponding to a CAV servo pattern, can be read by reading means synchronized to the same data clock as used for data recorded in the track portion adjoining the header. This is advantageous in that only one phase locked loop is required to generate the data clock locked to the data speed.
The invention is also based on the following recognition relating to the overhead and reduced data storage capacity incurred by applying headers. Headers in the servo pattern are used to indicate the location of data to be recorded, which data is usually subdivided in logical units called sectors. For example D1 describes a zoned disc having in each zone a fixed number of data sectors fitting in one turn of the track and one header per turn, the first sector starting at said one header. In our invention several headers are required in one turn for fast access to the data after a jump to a new radial position, because otherwise the device would have to wait maximally almost a full rotation of the disc before a header can be read. In known disc formats, such as DVD-RAM and shown in FIG. 2, a number of headers per turn is used in a CLV pattern, i.e. aligned with the sectors and therefore a radially outward increasing number of headers per turn of the track. A relative large header overhead is caused by the CLV header pattern. According to our invention a number of headers in each turn being aligned radially in a CAV servo pattern allow fast recovery of the radial and angular position of the scanning unit. A high average density of data recording is achieved by recording in each track portion an amount of data proportional to the radial position of the track portion concerned causing CLV data density. In particular the inventors have seen, that the disc format can be used for recording data blocks in logical sectors in the following way. The size of the logical sectors is selected independent of the distance between headers and the start of sectors is not necessarily at the headers. Contrary to the CAV system the start of a sector is positioned at an arbitrary location relative to the beginning of the recording area, calculated from the known amounts of data in each preceding track portion. The headers are used only to determine the position of the scanning unit, and the start of a sector is located for example at m channel bits after header n. Hence in the new disc format headers may interrupt a sector at one or more arbitrary locations. However, as the headers are provided at the same density as the data of the sectors, they can be read by the data reading means, recognized as being headers and eliminated from the recovered data. So the number of headers is relatively low and adjusted to the requirements of fast positioning. The low header overhead is advantageous for the total available storage capacity of the disc and therefore for the average density.
An embodiment of the optical disc is characterized in that the recording area is subdivided in a plurality of coaxial annular zones, each track portion within one of the zones for recording a same predetermined amount of data at a track portion density, the average of track portion densities within one zone being substantially equal to said constant density. This has the advantage that the amount of data within each track portion within one of the zones is constant.
A further embodiment of the optical disc is characterized in that the track portions comprise periodic characteristics indicative of the density for the respective track portion. This has the advantage, that a data clock of the required frequency can be generated by a phase locked loop locked to the periodic characteristics. It is to be noted, that the periodic characteristics are available for recorded and unrecorded parts of the recorded area, whereby the headers can be read reliably also in unrecorded areas.
Further advantageous, preferred embodiments of the apparatus and detection unit according to the invention are given in the dependent claims.
These and other aspects of the invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which
FIG. 1 shows a record carrier,
FIG. 2 shows a prior art optical disc with a CLV header pattern,
FIG. 3 shows a zoned optical disc,
FIG. 4 shows a header and sector layout,
FIG. 5 shows an apparatus for reading a record carrier,
FIG. 6 shows an apparatus for writing and reading a record carrier, and
FIG. 7 shows a land/groove servo pattern at a zone boundary.